D
Glossary and Acronyms


Background radiation (cosmic)—

The radiation left over from the Big Bang explosion at the beginning of the universe. As the universe expanded, the temperature of the fireball cooled to its present level of 2.7 degrees above absolute zero.

Brown Dwarf—

A star-like object that contains less than about 0.08 the mass of the Sun and is thus too small to ignite nuclear fuels and become a normal star. Brown dwarfs emit small amounts of infrared radiation due to the slow release of gravitational energy.


Dark energy—

An as yet unknown form of energy that pervades the universe. Its presence was inferred from the discovery that the expansion of the universe is accelerating, and these observations suggest that about 70 percent of the total density of matter plus energy is in this form. One explanation for dark energy is Einstein’s cosmological constant.


Flat universe—

Cosmological concept that states that the universe will expand forever at a decelerating rate, and will never pass an outer limit.


Gamma-ray bursts—

A sudden burst of gamma rays coming from a source usually in deep space. The burst may last from a fraction of a second to several minutes.

Gravitational microlensing—

Gravitational lensing due to a stellar mass object. This lensing phenomenon is termed “microlensing” because the mass of the lens is so small compared with that of a galaxy.



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U.S. Astronomy and Astrophysics: Managing an Integrated Program D Glossary and Acronyms Background radiation (cosmic)— The radiation left over from the Big Bang explosion at the beginning of the universe. As the universe expanded, the temperature of the fireball cooled to its present level of 2.7 degrees above absolute zero. Brown Dwarf— A star-like object that contains less than about 0.08 the mass of the Sun and is thus too small to ignite nuclear fuels and become a normal star. Brown dwarfs emit small amounts of infrared radiation due to the slow release of gravitational energy. Dark energy— An as yet unknown form of energy that pervades the universe. Its presence was inferred from the discovery that the expansion of the universe is accelerating, and these observations suggest that about 70 percent of the total density of matter plus energy is in this form. One explanation for dark energy is Einstein’s cosmological constant. Flat universe— Cosmological concept that states that the universe will expand forever at a decelerating rate, and will never pass an outer limit. Gamma-ray bursts— A sudden burst of gamma rays coming from a source usually in deep space. The burst may last from a fraction of a second to several minutes. Gravitational microlensing— Gravitational lensing due to a stellar mass object. This lensing phenomenon is termed “microlensing” because the mass of the lens is so small compared with that of a galaxy.

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U.S. Astronomy and Astrophysics: Managing an Integrated Program Microlensing of distant stars by intervening faint stars can reveal planets in orbit around the lensing star. Interferometry— The main technique used by astronomers to map sources at high resolution and to measure their positions with high precision. Kuiper Belt objects (KBOs)— Icy planetesimals distributed in a roughly circular disk in the outer regions of our solar system, 50 to 100 AU from the Sun. Redshift— Radiation from an approaching object is shifted to higher frequencies (to the blue), while radiation from a receding object is shifted to lower frequencies (to the red). A similar effect raises the pitch of an ambulance siren as it approaches. The expansion of the universe makes objects recede so that the light from distant galaxies is redshifted. The redshift is often denoted by z, where z=v/c and v is the velocity and c the speed of light. AAPB Astronomy and Astrophysics Planning Board AASC NRC Astronomy and Astrophysics Survey Committee ACAST Advisory Committee for AST (NSF Astronomical Sciences Division) ACCORD AURA Coordinating Council of Observatory Research Directors ALMA Atacama Large Millimeter Array ARISE Advanced Radio Interferometry between Space and Earth AST Advanced Solar Telescope (now called the Advanced Technology Solar Telescope, or ATST); NSF Astronomical Sciences Division ATM NSF Division of Atmospheric Sciences AURA Associated Universities for Research in Astronomy, Inc. CAA NRC Committee on Astronomy and Astrophysics CARMA Combined Array for Research in Millimeter-wave Astronomy CGRO Compton Gamma-Ray Observatory COMRAA Committee on the Organization and Management of Research in Astronomy and Astrophysics DOE U.S. Department of Energy EVLA Expanded Very Large Array EXIST Energetic X-ray Imaging Survey Telescope FASR Frequency Agile Solar Radio telescope

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U.S. Astronomy and Astrophysics: Managing an Integrated Program GBT Green Bank Telescope (now named after Senator Robert C. Byrd) GLAST Gamma-ray Large Area Space Telescope GSMT Giant Segmented Mirror Telescope HENP DOE Office of High Energy and Nuclear Physics HEP DOE Division of High Energy Physics HEPAP High Energy Physics Advisory Panel HST Hubble Space Telescope LIGO Laser Interferometer Gravitational-Wave Observatory LISA Laser Interferometer Space Antenna LSST Large-aperture Synoptic Survey Telescope MPS NSF Mathematical and Physical Sciences Directorate MPSAC MPS Advisory Committee MRE NSF Major Research Equipment line NASA National Aeronautics and Space Administration NGST Next Generation Space Telescope NOAO National Optical Astronomy Observatory NRAO National Radio Astronomy Observatory NRC National Research Council NRL Naval Research Laboratory NSAC Nuclear Science Advisory Committee NSF National Science Foundation NSO National Solar Observatory NVO National Virtual Observatory OMA NSF Office of Multidisciplinary Affairs OMB Office of Management and Budget OPP NSF Office of Polar Programs OSS NASA Office of Space Science OSTP Office of Science and Technology Policy ROTSE Robotic Optical Transient Search Experiment SAFIR Single Aperture Far Infrared observatory SAGENAP Science Assessment Group for Experiments in Non-Accelerator Physics SDO Solar Dynamics Observatory SKA Square Kilometer Array SPST South Pole Submillimeter-wave Telescope

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U.S. Astronomy and Astrophysics: Managing an Integrated Program SSB NRC Space Studies Board SScAC NASA Space Science Advisory Committee TPF Terrestrial Planet Finder TSIP NSF Telescope System Instrumentation Program VERITAS Very Energetic Radiation Imaging Telescope Array System VLA Very Large Array